What A1C misses
Two people with the same A1C can have very different glucose patterns — one steady, one swinging between highs and lows. Continuous glucose monitoring adds time-in-range and variability, which A1C alone cannot show.
- • Red blood cell lifespan variation shifts A1C independent of glucose.
- • Time-in-range of 70–180 mg/dL is the modern complement to A1C.
- • Fasting glucose and OGTT can disagree with A1C; clinicians use all three.
FAQ
What does an A1C of 5.9 mean?
It corresponds to an estimated average glucose of about 123 mg/dL and falls in the prediabetes range of 5.7–6.4%. It warrants a conversation with a clinician about lifestyle and repeat testing.
How quickly can A1C change?
Meaningful movement takes 8–12 weeks because A1C reflects the lifespan of red blood cells. Retesting sooner than three months rarely adds information.
Is estimated average glucose the same as a meter reading?
No. eAG is the average across all times of day including sleep, so it is usually lower than typical post-meal fingerstick readings.
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